Oocyte-specific gene expression: molecular characterization of a cDNA coding for ZP-3, the sperm receptor of the mouse zona pellucida.

The mouse zona pellucida genes are expressed uniquely during oogenesis and are developmentally regulated in the absence of cell division. Little is known about the mechanisms that control the expression of these germ-line-specific genes that play crucial roles in early mammalian development. We have constructed a lambda gt11 cDNA library from ovarian poly(A)+ mRNA and have isolated clones coding for ZP-3, the mouse sperm receptor. The identity of the clones was confirmed by comparing their DNA sequence with an amino acid sequence obtained from an isolated ZP-3 peptide. The ZP-3 gene is transcribed as a 1.7-kilobase poly(A) mRNA that is detected exclusively in ovarian tissue. This germ-line-specific expression is reflected in the observed hypomethylation of the ZP-3 locus in ovarian but not liver or brain DNAs. The ZP-3 gene is otherwise identically organized in somatic and germ-line DNA where it appears to be present as a low-copy-number or single-copy gene. Despite the fact that the mouse sperm receptor demonstrates species specificity, the ZP-3 cDNA cross-hybridized with DNA from a variety of mammalian species, including rat, rabbit, dog, pig, cow, and human.